In manga, there's always a character who gets a sudden boost of power, right? Usually, it's when they're driven into a corner. Readers actually call it a "convenient power up", but it actually does happen in the real world as well. We humans only truly show our mettle when we're pushed into a corner.
Crying is the same thing as pouring all your frustations and regrets out of your body. You may use it as a weapon, but that's just too easy. Whenever you feel like crying, just smile instead. That's what it means to be a man. You get it?
Humans are so voracious, though. They eat everything from plants to animals... almost as if they think they are the top living creature to roam the earth. No being is more full of themselves as the humans.